A traffic jam may refer to a situation in which there is high vehicle congestion with minimal flow. Gridlock may be defined as a type of traffic jam where continuous queues of vehicles block an entire network of intersecting streets, thereby bringing traffic in all directions to a standstill. Traditionally, gridlock is caused by traffic heading in one direction across an intersection, and then the traffic being stopped due to a blockage in the intersection. The blockage may result from, for example, vehicle overcapacity and vehicle accident. Gridlock is cited as example of a “prisoner's dilemma” problem of game theory. Mutual cooperation among drivers would provide the maximum benefit (e.g., prevention of gridlock), but such mutual cooperation may not happen due to individual drivers seeking to maximize their own benefit (e.g., shortest travel time) given the uncertainty about the other drivers' commitments to mutual cooperation.
To combat gridlock, many jurisdictions have enacted rules prohibiting motorists from entering an intersection at a green light, if there is no room for them to clear the intersection, in the prevention of what is colloquially known as “blocking the box.” Adhering to these rules minimizes the occurrence of gridlock and traffic will only slow in the direction that is actually congested. Additionally, a box junction may be utilized to reduce gridlock. A box junction is a road traffic control measure provides drivers with a clear visualization as to where the junction is. The surface of the box junction is typically marked with a crisscross grid of diagonally painted lines (or only two lines crossing each other in the box). Vehicles may not enter the marked area unless their exit from the junction is clear or, if turning, to await a gap in the oncoming traffic flow.